Soft PLC Technology Development And Research

Soft PLC technology is one of currently hotspots in industrial automation research , compared with the traditional hardware PLC, soft PLC is open architecture, stronger network communication ability and the data processing ability, can better meet the requirement of modern industrial automation. Soft PLC will put all the programs which operation, calculation and data processing functions by hardware PLC to PC or embedded computer to do, and data acquisition and output be done by external I/O boards. In this process, how to make the traditional PLC language (ladder diagram and statements) can be identified and be correct implemented by PC or other hardware platform becomes a key of this system. Therefore, it is necessary to develop a correct and efficient execution user program compiles system.From compile system's nature, there a tow kinds compiles, translation and interpretation of compiler, compiled by these two kinds of for their advantages and disadvantages, we select explanation compiler, preview compiler will troubleshoot the user PLC program and turn it in simple middle code, then the explain system will operation explanation. Based on sentence semantic analysis and understanding with each instruction sheet language of IEC61131-3 standard, we develop the explanation compiler system for pick and circulation the user program to interpreting and executing, and get same operation results with traditional hardware PLC. Compared with transplantation compiler, explanation compiler can be easily realized portability to different hardware platform.Based on VC + + 6.0 for development tool, the soft PLC system and the system in the following IEC61131-3, and provides ladder-diagram programming list statements/ladder diagram procedures and statements, the conversion tables to compile programs, related operation function.This paper works are as follows:(1) Compare soft PLC with traditional hardware PLC for the advantages and disadvantages, Explained the necessity of develop a based on PC soft PLC system. Explained the realization of ladder-diagram editor, instruction form editor, and ladder-diagram form to statement.(2) After compared translation type compiler and explanation type compiler, choose the explanation type compiler to develop the soft PLC compiler system.(3) Developed the explain operation system of soft PLC based on VC++6.0 development platform. Described the Grammatical analysis, the semantic analysis and intermediate code generation process. Described the method how Soft PL system access external I/O devices.(4) Given the realization method of part of logical operation instructions of PLC. By actual testing, this soft PLC compiled satisfied the requirement of this topic; achieve the soft PLC program compiled for users, and the I/O devices for data exchange.